Anti-reflective coating compositions comprising polymerized aminoplasts

ABSTRACT

Improved anti-reflective coating compositions for use in integrated circuit manufacturing processes and methods of forming these compositions are provided. Broadly, the compositions are formed by heating a solution comprising a compound including specific compounds (e.g., alkoxy alkyl melamines, alkoxy alkyl benzoguanamines) under acidic conditions so as to polymerize the compounds and form polymers having an average molecular weight of at least about 1,000 Daltons. The monomers of the resulting polymers are joined to one another via linkage groups (e.g., —CH 2 —, —CH 2 —O—CH 2 —) which are bonded to nitrogen atoms on the respective monomers. The polymerized compound is mixed with a solvent and applied to a substrate surface after which it is baked to form an anti-reflective layer. The resulting layer has high k values and can be formulated for both conformal and planar applications.

This application is a divisional of U.S. patent application Ser. No.09/552,236, filed Apr. 19, 2000, now U.S. Pat. No. 6,323,310incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly concerned with anti-reflectivecompositions and methods of forming the compositions for use asanti-reflective coating (ARC) layers on substrates during integratedcircuit manufacturing processes. More particularly, the inventivecompositions are formed by polymerizing aminoplasts (eg., melamine,benzoguanamine) in an acidic environment under elevated temperatures toyield cross-linkable, UV absorbing, fast etching compositions.

2. Description of the Prior Art

A frequent problem encountered by photoresists during the manufacturingof semiconductor devices is that activating radiation is reflected backinto the photoresist by the substrate on which it is supported. Suchreflectivity tends to cause blurred patterns which degrade theresolution of the photoresist. Degradation of the image in the processedphotoresist is particularly problematic when the substrate is non-planarand/or highly reflective. One approach to address this problem is theuse of a bottom anti-reflective coating (BARC) applied to the substratebeneath the photoresist layer.

Fill compositions which have high optical density at the typicalexposure wavelengths have been used for some time to form these BARClayers. The BARC compositions typically consist of an organic polymerwhich provides coating properties and a dye for absorbing light. The dyeis either blended into the composition or chemically bonded to thepolymer. Thermosetting BARC's contain a cross-linking agent in additionto the polymer and dye. Cross-linking must be initiated, and this istypically accomplished by an acid catalyst present in the composition.As a result of all these ingredients which are required to performspecific and different functions, prior art BARC compositions are fairlycomplex.

U.S. Pat. No. 5,939,510 to Sato et al. discloses a BARC compositionwhich comprises a UV absorber and a cross-linking agent. The UV absorberis a benzophenone compound or an aromatic azomethine compound having atleast one unsubstituted or alkyl-substituted amino group on the arylgroups. The cross-linking agent disclosed by Sato et al. is a melaminecompound having at least two methylol groups or alkoxymethyl groupsbonded to the nitrogen atoms of the molecule.

The Sato et al. composition suffers from two major drawbacks. First, inthe two-component composition disclosed, the Sato et al. compositiondoes not include a polymeric material thus resulting in insufficientcoverage on the surfaces and edges of the substrate features.Furthermore, the UV absorber disclosed by Sato et al. is physicallymixed with the cross-linking agent rather than chemically bonded to somecomponent of the composition. As a result, the UV absorber will oftensublime, and in many cases sublime and diffuse into the subsequentlyapplied photoresist layer.

There is a need for a less complex anti-reflective composition whichprovides high reflection control and increased etch rates whileminimizing or avoiding intermixing with photoresist layers.

SUMMARY OF THE INVENTION

The present invention overcomes these problems by broadly providingimproved anti-reflective compositions which are formed from a minimalnumber of components (e.g., two or less) and which exhibit theproperties necessary in an effective BARC composition.

In more detail, anti-reflective compositions according to the inventioninclude polymers comprising monomers derived from compounds of Formula Iand mixtures thereof.

wherein each X is individually selected from the group consisting of NR₂(with the nitrogen atom being bonded to the ring structure) and phenylgroups, where each R is individually selected from the group consistingof hydrogen, alkoxyalkyl groups, carboxyl groups, and hydroxymethylgroups. Preferred compounds of Formula I include the following:

When used in reference to Formula I, the phrase “monomers derived fromcompounds of Formula I” is intended to refer to functional moieties ofFormula I. For example, each of the structures of Formula II is derivedfrom compounds of Formula I.

wherein: each X is individually selected from the group consisting ofNR₂ (with the nitrogen atom being bonded to the ring structure) andphenyl groups, where each R is individually selected from the groupconsisting of hydrogen, alkoxyalkyl groups, carboxyl groups, andhydroxymethyl groups; and “M₁” and “M₂” represent a molecule (e.g., achromophore or another monomer derived from the compound of Formula I)bonded to X′ or X″. Thus, “monomers derived from the compounds ofFormula I”. would include those compounds where any of the constituents(i.e., any of the X groups, and preferably 1-2 of the X groups) isbonded to another molecule.

The polymerized monomers are preferably joined by linkage groupsselected from the group consisting of —CH₂—, —CH₂—O—CH₂, and mixturesthereof, with the linkage groups being bonded to nitrogen atoms on therespective monomers. For example, Formula III demonstrates twomethoxymethylated melamine moieties joined via a —CH₂— linkage group andtwo methoxymethylated melamine moieties joined via a —CH₂—O—CH₂— linkagegroup.

Formula IV illustrates two benzoguanamine moieties joined via CH₂linkage groups.

Finally, Formula V illustrates two methoxymethylated melamine moietieshaving a chromophore (2,4-hexadienoic acid) bonded thereto and joinedvia CH₂ linkage groups.

The inventive compositions are formed by providing a dispersion of thecompounds of Formula I in a dispersant (preferably an organic solventsuch as ethyl lactate), and adding an acid (such as p-toluenesulfonicacid) to the dispersion either prior to or simultaneous to heating ofthe dispersion to a temperature of at least about 70° C., and preferablyat least about 120° C. The quantity of acid added should be from about0.001-1 moles per liter of dispersant, and preferably from about0.01-0.5 moles of acid per liter of dispersant. Furthermore, the heatingstep should be carried out for at least about 2 hours, and preferablyfrom about 4-6 hours. In applications where only benzoguanamine-basedmoieties are utilized, the heating step should be carried out for a timeperiod of less than about 7 hours, and preferably from about 5.5-6.5hours.

Heating the starting compounds under acidic conditions causes thecompounds to polymerize by forming the previously described linkagegroups. The polymers resulting from the heating step should have anaverage molecular weight of at least about 1,000 Daltons, preferably atleast about 5,000 Daltons, and more preferably at least about5,000-20,000 Daltons. Furthermore, about 12 hours after the heating stepthe resulting anti-reflective composition should have a decrease of atleast about 20%, preferably at least about 40%, and more preferably fromabout 40-70% in methoxymethylol (—CH₂OCH₃) groups than were present inthe starting dispersions of Formula I compounds, with the quantity ofmethoxymethylol groups being determined by the titration procedure asherein defined.

It will be appreciated that the inventive polymer compositions providesignificant advantages over prior art compositions in that thepolymerized compositions alone act as conventional anti-reflectivecoating polymer binders, cross-linking agents, and chromophores, thusgreatly simplifying the anti-reflective coating system.

In applications where enhanced light absorbance is desired, achromophore (e.g., 2,4-hexadienoic acid, 3-hydroxy-2-naphthoic acid) canbe mixed with the starting dispersion prior to acid and heat treatment.During subsequent acid treatment, the chromophore will chemically bondto the monomers during polymerization.

The resulting polymerized composition is mixed with a solvent to form ananti-reflective coating composition. Suitable solvents include propyleneglycol monomethyl ether, propylene glycol monomethyl ether acetate,ethyl lactate, and cyclohexanone. The anti-reflective coatingcomposition is subsequently applied to the surface of a substrate (e.g.,silicon wafer) by conventional methods, such as by spin-coating, to forman anti-reflective coating layer on the substrate. The substrate andlayer combination is baked at temperatures of at least about 160° C. Thebaked layer will generally have a thickness of anywhere from about 500 Åto about 2000 Å.

In an alternate embodiment, an anti-reflective composition is formed bypreparing a dispersion including, in a dispersant (e.g., propyleneglycol monomethyl ether, propylene glycol monomethyl ether acetate,ethyl lactate), a quantity of the compound of Formula I and a polymerhaving cross-linking sites therein. The composition should comprise atleast about 1.5% by weight of the polymer, and preferably from about2.0-20% by weight of the polymer, based upon the total weight of thesolids in the composition taken as 100% by weight. The molecular weightof the polymer is at least about 2,000 Daltons, and preferably fromabout 5,000-100,000 Daltons. The cross-linking sites on the polymerpreferably comprise a cross-linking group selected from the groupconsisting of hydroxyl, carboxylic, and amide groups. The most preferredpolymers include cellulose acetate hydrogen phthalate, cellulose acetatebutyrate, hydroxypropyl cellulose, ethyl cellulose, polyesters,polyacrylic acid, and hydroxypropyl methacrylate.

In this embodiment, it is not necessary to heat the dispersion. However,as was the case with the first embodiment, the composition preferablyincludes an acid such as p-toluenesulfonic acid. Advantageously, it isnot necessary to add a chromophore to the composition as the compound ofFormula I also functions as a light-absorber. Thus, the composition ispreferably essentially free (i.e., less than about 0.5% by weight,preferably less than about 0.1% by weight, and more preferably about 0%by weight) of any added chromophores.

In either embodiment, low molecular weight (e.g., less than about 13,000Daltons) polymeric binders can be utilized in the dispersion (afterheating and acidification steps in the case of the first embodiment) toassist in forming highly planar layers. Alternately, a high molecularweight polymeric binder (e.g. acrylics, polyester, or cellulosic polymersuch as cellulose acetate hydrogen phthalate, hydroxypropyl cellulose,and ethyl cellulose) having a molecular weight of at least about 100,000Daltons can be mixed with the starting dispersion (also after heatingand acidification steps in the case of the first embodiment) to assistin forming conformal layers. This will result in an anti-reflectivelayer having a percent conformality of at least about 60%, even ontopographic surfaces (i.e., surfaces having raised features of 1000 A orgreater and/or having contact or via holes formed therein having holedepths of from about 1000-15,000 Å).

As used herein, percent conformality is defined as:$100 \cdot \frac{\begin{matrix}\left| {\left( {{thickness}\quad {of}\quad {the}\quad {film}\quad {at}\quad {location}\quad A} \right) -} \right. \\\left. \left( {{thickness}\quad {of}\quad {the}\quad {film}\quad {at}\quad {location}\quad B} \right) \right|\end{matrix}}{\left( {{thickness}\quad {of}\quad {the}\quad {film}\quad {at}\quad {location}\quad A} \right),}$

wherein: “A” is the centerpoint of the top surface of a target featurewhen the target feature is a raised feature, or the centerpoint of thebottom surface of the target feature when the target feature is acontact or via hole; and “B” is the halfway point between the edge ofthe target feature and the edge of the feature nearest the targetfeature. “Feature” and “target feature” is intended to refer to raisedfeatures as well as contact or via holes. As also used in thisdefinition, the “edge” of the target feature is intended to refer to thebase of the sidewall forming the target feature when the target featureis a raised feature, or the upper edge of a contact or via hole when thetarget feature is a recessed feature. Percent planarization is definedas:

100-% conformality.

Regardless of the embodiment, anti-reflective layers formed according tothe invention will absorb at least about 90%, and preferably at leastabout 95%, of light at wavelengths of from about 190-260 nm.Furthermore, the anti-reflective layers have a k value (i.e., theimaginary component of the complex index of refraction) of at leastabout 0.2, and preferably at least about 0.5, at the wavelength ofinterest. Finally, the anti-reflective layers have high etch rates,particularly when melamine is utilized. The etch selectivity to resistwill be at least about 1.5, and preferably at least about 2.0 when CF₄is used as the etchant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting the molecular weight distribution ofpolymerized Cymel® 303 as a function of reaction time;

FIG. 2 is a graph depicting the molecular weight distribution ofpolyrnerized Cymel® 303 having 3-hydroxy-2-naphthoic acid bonded theretoas a function of reaction time; and

FIG. 3 is a graph depicting the change in the methylol andmethoxymethylol groups over time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

The following examples set forth preferred methods in accordance withthe invention. It is to be understood, however, that these examples areprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

Testing Procedures

1. Stripping Test Procedure

In the following examples, a stripping test was performed to determinethe resistance of the experimental anti-reflective coating (ARC) tophotoresist solvents. In this procedure, an ARC formulation wasspin-coated onto a silicon wafer at a spin speed of 2,500 rpm for 60seconds and at an acceleration of 20,000 rpm/second. The film was bakedon a hotplate at 205° C. for 60 seconds. The ARC film thickness was thenmeasured at multiple points on the wafer using ellipsometry.

Ethyl lactate was puddled onto the silicon wafer for 10 seconds,followed by spin drying at 3,500 rpm for 30 seconds to remove thesolvent. The film was then baked on a hotplate at 100° C. for 30seconds. The ARC film thickness was again measured at multiple points onthe wafer using ellipsometry. The amount of stripping was determined tobe the difference between the initial and final average filmthicknesses, with the uncertainty in the stripping measurement being thesum of the two average thickness measurement uncertainties.

2. Interlayer Formation Procedure

In the following examples, the degree of intermixing between the sampleARC and the photoresist was determined. In this procedure, an ARCformulation was spin-coated onto a silicon wafer at a spin speed of2,500 rpm for 60 seconds and at an acceleration of 20,000 rpm/second.The film was baked on a hotplate at 205° C. for 60 seconds. The ARC filmthickness was then measured at multiple points on the wafer usingellipsometry.

A photoresist (UV6, available from Shipley) was spin-coated on top ofthe ARC film at a spin speed of 3250 rpm for 30 seconds and at anacceleration of 20,000 rpm/second under ambient conditions. The waferwas then baked on a hotplate for 130° C. for 60 seconds and exposed to20 mJ of exposure energy, after which a post-exposure bake was performedon the wafer at 130° C. for 90 seconds.

The photoresist was developed with Shipley LDD26W developer for 40seconds. The sample was then rinsed with distilled water and spun dry at2,000 rpm for 20 seconds followed by baking on a hotplate for 100° C.for 30 seconds. The film thickness was again measured at multiple pointson the wafer using ellipsometry. The difference in the two filmthickness averages (Å) was recorded as the interlayer stripping resultwith the uncertainty in the interlayer measurement being the sum of thetwo average thickness measurement uncertainties.

3. Titration Procedure

a. Free Formaldehyde Analysis

A 10% Na₂SO₃ (aq) solution was prepared by mixing 50 g of Na₂SO₃ with450 g of water. A few drops of rosolic acid was added to this solutionuntil it turned red after which 1N HCl (aq) was added to the solutionuntil it turned to a color between pale pink and colorless. The shelflife of the resulting solution is 2-3 days.

The sample to be tested was prepared by mixing 1.5 g of the sample with10 ml of 1,4-dioxane. Next, 20 g of the previously prepared 10% Na₂SO₃solution was added to the flask and the flask was agitated with amagnetic stirrer. While stirring, 1N HCl (aq) was titrated into theflask until the solution turned pale pink or colorless. The freeformaldehyde was then determined by the following equation:

 Y=[(A−BL)*(30.03/1000)*100]/W,

where “A” is the amount (in ml) of titrated 1N HCl, “BL” is the amount(in ml) titrated for a blank (i.e., 1,4-dioxane only), “W” is the weightof the sample in grams, and “Y” is the weight percent of freeformaldehyde in the solution. Thus, the total free formaldehyde weight(X) is:

[(total solution weight in )*(Y)]100.

b. —CH₂OH Analysis

In this procedure, 1 g of the sample was mixed with 20 ml of 1,4-dioxanein a beaker followed by sonication for two minutes. The solution wasthen transferred to a flask, and the beaker was rinsed three times with10 ml portions of water (for a total of 30 ml), with the rinse waterbeing added to the flask after each rinsing. Next, 25 ml of I₂ (0.1N)and 10 ml of 2N NaOH (aq) were added to the solution, the flask wascapped tightly, and the solution was allowed to stand for 10 minutes.The solution was then titrated with 0.1N Na₂S₂O₃ (aq) until it turned apurple-brown color. The percent —CH₂OH was then determined according tothe following equation:

% —CH₂OH=(B−A)*0.1*(1.502/weight of sample in g)−X,

where “A” is the amount (in ml) titrated for a blank (i.e., 1,4-dioxaneonly), “B” is the amount (in ml) of titrated 0.1N Na₂S₂O₃, and “X” isthe total free formaldehyde weight determined as described in part (a)above.

c. —CH₂OCH₃ Analysis

In this procedure, 1 g of the sample was mixed with 20 ml of 1,4-dioxanein a beaker followed by sonication for two minutes. The solution wasthen transferred to a flask, and the beaker was rinsed three times with10 ml portions of water (for a total of 30 ml), with the rinse waterbeing added to the flask after each rinsing. Next, 20 ml of 2N of H₂SO₄(aq) was added to the flask and the solution was allowed to stand for 20minutes at a temperature of 30-35° C. To the solution, 25 ml of I₂(0.1N) and 25 ml of 2N NaOH (aq) were added, the flask was cappedtightly, and the solution was allowed to stand for 15 minutes at roomtemperature. An additional 20 ml of 2N H₂SO₄ (aq) was mixed with thesolution, and the solution was titrated with 0.1N Na₂S₂O₃ (aq) until itturned from a purple-brown color to colorless. The percent —CH₂OCH₃ wasthen determined according to the following equation:

% —CH₂OCH₃=(B−A)*0.1*(1.502/weight of sample in g)−X,

where “A” is the amount (in ml) titrated for a blank (i.e., 1,4-dioxaneonly), “B” is the amount (in ml) of titrated 0.1N Na₂S₂O₃, and “X” isthe total free formaldehyde weight determined as described in part (a)above.

Example 1

Cymel® 303 (40.0 g, available from Cytec Industries, Inc., New Jersey)was dissolved in 180.0 g of ethyl lactate in a 500 ml round-bottomedflask. In a 50 ml beaker, 1.0 g of p-toluenesulfonic acid (PTSA) wasdissolved in 20 g of ethyl lactate. The round-bottomed flask was fittedwith a nitrogen source, a water condenser, and a thermometer, and thecontents of the flask heated to 120° C. in an oil bath. The pTSAsolution was added to the beaker via an addition funnel. The resultingsolution was maintained at a temperature of 120° F. for 12 hours. Duringthis 12-hour time period, 50 g aliquots of the solution were collectedat 0 hours, 4 hours, 6 hours, 8 hours, and 12 hours, and labeled asSamples 1-5, respectively.

Each of the samples was cooled and filtered through a 0.1 micron filter.An anti-reflective coating was formulated from the cooled samples 1-5 byadding 73.0 g of propylene glycol monomethyl ether (PGME) to the cooledand filtered samples. The molecular weight distribution profiles ofthese samples were determined using a gel permeation chromatograph witha refractive index detector and 50 Å, 100 Å, and 500 Å Phenogel(Phenomenex) columns in series. These results are shown in FIG. 1.

Silicon wafers were spin-coated with each of the above formulations at2500 rpm for 60 seconds followed by drying and baking at 205° C. for 60seconds. The film thickness was measured, and the optical parameters ofthe film were determined. This data is reported in Table 1. The etchselectivity to resist (DUV42) with CF₄ as the etchant was 1.52.

TABLE 1 Reaction Stripping Interlayer time Thickness Test Test Sample(hours) Å n k Å Å 1 0 1341 2.08 0.182  −2 ± 11 30 ± 34 2 4 1657 2.070.247 −88 ± 41 84 ± 42 3 6 1728 2.08 0.229 −20 ± 17 93 ± 15 4 8 17412.07 0.237 −23 ± 21 92 ± 21 5 12 1877 2.07 0.237 −14 ± 13 101 ± 38 

Example 2

Cymel® 303 (40.0 g) and 8.0 g of 3-hydroxy 2-naphthoic acid weredissolved in 180.0 g of ethyl lactate in a 500 ml round-bottomed flask.In a 50 ml beaker, 1.0 g of pTSA was dissolved in 20 g of ethyl lactate.The round-bottomed flask was fitted with a nitrogen source, a watercondenser, and a thermometer, and the contents of the flask heated to120° C. in an oil bath. The pTSA solution was added to the beaker via anaddition funnel. The resulting solution was maintained at a temperatureof 120° F. for 12 hours. During this 12-hour time period, 50 g aliquotsof the solution were collected at 0 hours, 4 hours, 6 hours, 8 hours,and 12 hours, and labeled as Samples 1-5, respectively.

Each of the samples was cooled and filtered through a 0.1 micron filter.An anti-reflective coating was formulated from samples 1-5 by adding73.0 g of PGME to the cooled and filtered samples. The molecular weightdistribution profiles of these samples were determined using a gelpermeation chromatograph with a refractive index detector and 50 Å, 100Å, and 500 Å Phenogel columns in series. These results are shown in FIG.2.

Silicon wafers were spin-coated with each of the above formulations at2500 rpm for 60 seconds followed by drying and baking at 205° C. for 60seconds. The film thickness was measured, and the optical parameters ofthe film were determined. This data is reported in Table 2. The etchselectivity to resist (DUV42) with CF₄ as the etchant was 1.40.

TABLE 2 Reaction Stripping Interlayer time Thickness Test Test Sample(hours) Å n k Å Å 1 0 2255 2.08 0.477 −4 ± 17 40 ± 64 2 4 2021 2.070.459   2 ± 17 61 ± 27 3 6 1928 2.08 0.469 −2 ± 8  61 ± 34 4 8 1926 2.080.468 −7.8 ± 63 ± 11 13 5 12 1957 2.07 0.461   8.8 ± 50 ± 49  0

Example 3

Cymel® 303 and Cymel® 1123 (see Table 3 for amounts) were dissolvedalong with 0.75 g of pTSA were dissolved in 150.0 g of ethyl lactate ina 500 ml round-bottomed flask. The flask was fitted with a nitrogensource, a water condenser, and a thermometer after which the flaskcontents were heated to 120° C. in an oil bath and maintained at thistemperature for 12 hours. The sample was filtered through a 0.1 micronfilter. An anti-reflective coating was formulated by adding PGME,p-toluenesulfonate or pyridine, and pyridinium tosylate (pPTS) to theprepared sample in the amounts indicated in Table 3.

The formulations were spin-coated on silicon wafers at 2500 rpm for 60seconds followed by drying and baking at 205° C. for 60 seconds. Therespective thicknesses of the films were measured, and the opticalparameters were determined. This data is reported in Table 4.

TABLE 3 For- Cy- Cy- Total mula- mel ® mel ® Ethyl Total tion 303 1123PGME lactate pyridine pPTS pTSA I 10 g 20 g 336.2 g 247.6 g — —   2 g II25 g  5 g 336.3 g 247.6 g — —   2 g III 10 g 20 g 336.2 g 247.6 g 0.3 g1.65 g 0.75 g IV 25 g  5 g 336.2 g 247.6 g 0.3 g 1.65 g 0.75 g

TABLE 4 Formu- Thickness Stripping Interlayer Etch lation Å n k Test ÅTest Å Selectivity^(A) I 749 1.970 0.484 −2 39 1.3 II 720 2.106 0.363 030 1.6 III 747 1.945 0.461 2 40 1.3 IV 740 2.096 0.358 0 20 1.6^(A)Selectivity to resist (DUV42) with CF₄ as the etchant.

Example 4

Cellulose acetate hydrogen phthalate (3.0 g and having an averagemolecular weight of about 100,000 Daltons) was dissolved in 130.5 g ofPGME. Next, 11.5 g of Cymel® 1125, 5.0 g of Cymel® 303, 150 g ofpropylene glycol monomethyl ether acetate (PGMEA), and 1.15 g of pTSAwas added to the prepared solution and allowed to dissolve completely.The resulting solution was then filtered through a 0.1 micron.

The prepared formulation was spin-coated on silicon wafers at 2500 rpmfor 60 seconds followed by drying and baking at 205° C. for 60 seconds.The film thickness was measured, and the optical properties determined.This data is reported in Table 5. The percent conformality of the filmwas determined to be 60%.

TABLE 5 Thickness Å n k Stripping Test Å Interlayer Test Å 1280 1.920.35 0 ± 10 0 ± 40

Example 5

Cymel® 303 (25 g) and Cymel® 1123 (5 g) were dissolved along with 2 g ofpTSA in 247.6 g of ethyl lactate. The resulting mixture was heated to120° C., and the methylol and methoxymethylol groups were measured overtime according to above-defined titration procedure. These results areshown in FIG. 3. As indicated by these results, the methoxymethylolgroups decreased over time as the Cymel® polymerized. It is believedthat the methylol groups may be regenerating or that new methylol groupsare forming during polymerization since the methoxymethylol groups areinvolved in the polymerization.

We claim:
 1. A method of preparing a polymer composition and coating asurface with the polymer composition, said method comprising the stepsof: providing a dispersion including a quantity of a compound accordingto the formula:

wherein each X is individually selected from the group consisting of NR₂and phenyl groups, where each R is individually selected from the groupconsisting of hydrogen, alkoxyalkyl groups, carboxyl groups, andhydroxymethyl groups; adding to said dispersion from about 0.001-1 molesof an acid per liter of said dispersion; heating said dispersion to atemperature of at least about 70° C. for at least about 2 hours to yieldthe polymer composition; mixing the resulting polymer composition with asolvent so as to form an anti-reflective coating; and applying saidanti-reflective coating to the surface of a substrate to form a layer ofanti-reflective coating on said substrate surface.
 2. The method ofclaim 1, wherein said layer of anti-reflective coating has a k value ofat least about 0.2 when exposed to light having a wavelength of fromabout 190-260 nm.
 3. The method of claim 1, wherein said anti-reflectivecoating layer has an etch selectivity to resist of at least about 1.5when CF₄ is used as an etchant.
 4. The method of claim 1, wherein saidapplying step comprises spin-coating said anti-reflective coating onsaid substrate surface.
 5. The method of claim 1, wherein said solventis selected from the group consisting of propylene glycol monomethylether, propylene glycol monomethyl ether acetate, ethyl lactate, andcyclohexanone.
 6. The method of claim 1, further including the step ofbaking said anti-reflective coating layer after said applying step at atemperature of at least about 160° C.
 7. The method of claim 6, whereinsaid baked anti-reflective coating layer has a thickness of from about500-2,000 Å.
 8. The method of claim 1, further including the step ofmixing a polymer having an average molecular weight of at least about100,000 Daltons with said dispersion after said acid addition andheating steps.
 9. The method of claim 8, wherein said polymer isselected from the group consisting of cellulose acetate hydrogenphthalate, cellulose acetate butyrate, hydroxypropyl cellulose, ethylcellulose, hydroxypropyl methacrylate, polyacrylic acid, and polyesters.10. The method of claim 8, further including the step of: mixing theresulting polymer composition with a solvent so as to form ananti-reflective coating; applying said anti-reflective coating to thesurface of a substrate to form a layer of anti-reflective coating onsaid substrate surface; and baking said anti-reflective coating layerafter said applying step at a temperature of at least about 160° C.,said baked anti-reflective coating layer having a percent conformalityof at least about 60%.